This invention relates to an improved coupling for handling a workpiece and to an improved workpiece transfer means comprising such a coupling combined with a conveyor and to an improved workpiece handling method. One aspect of the invention relates to a coupling having workpiece detent means which move radially to grasp or release, as the case may be, a workpiece. An aspect of the invention relates to a combination of a workpiece coupling with a conveyor for moving the coupling in a timed manner between loading and unloading stations wherein the conveyor means additionally includes actuating means for operating the coupling to cause engagement and release of a workpiece. An aspect of the invention relates to a system for handling an easily marred workpiece such as one of plastic, soft metal, or the like while maintained in a substantially exact position for treatment during transfer.
The invention for purposes of illustration but not limitation will be described in connection with means for handling workpieces comprising injection molded plastic preforms that are being reheated to a carefully controlled temperature immediately prior to being blow molded into a bottle with a threaded neck for closure by a threaded closure. The preform has a circular cross-section and the parts of the coupling engaging the preform likewise have a circular cross-section.
Blow molding has assumed an increasingly important position in the art of manufacturing hollow articles such as containers from various plastics and resins such as polyethylene, polyvinyl chloride, polyacrylonitrile, polyethylene terephthalate and the like. The blow molding art has developed in two major directions depending on the way in which the working material is presented to the mold in which it is blown: extrusion blow molding and injection blow molding. The present invention as already indicated will be explained in connection with injection blow molding.
In injection blow molding, the plastic is first injection molded to make a preform. Where the end product is to be, for example, a bottle with a threaded neck, the injection molding yields the advantages of reducing thermal memory problems and providing a threaded neck which will not change significantly in shape or dimension during further processing.
After the preform has been made by injection molding it is removed to a blow molding operation where it is inserted in the mold, compressed gas such as clean compressed air is used to expand the preform into the shape of the mold and the completed container is recovered. It is often required to carefully regulate the temperature at which the preform is delivered to the blow mold. Temperature regulation is readily accomplished where injection and blowing are done on the same machine, often making use of the heat contained in the preform. Where, however, injection and blowing are done on different machines, a reheating procedure is required.
The present invention is particularly well suited conveying a preform through a reheating operation of the sort just described and delivering the same to a blow molding means. While so doing, it is to be understood that the preforms are passed through an oven where they are heated in a uniform manner. This is accomplished by engaging the preform with the aforesaid coupling, then (by means of the conveyor on which the coupling is mounted) passing it through an oven while continuously rotating the preform in order to heat it uniformly, removing same from the oven and releasing it from the coupling and the conveyor, and thereafter (although it forms no part of this invention) directing the preform into a blow molding system where it then is formed into a container.